The effect of tannic acid on GAs and cyclic-AMP promoted amylase induction in barley aleurone layers was examined. Of a variety of adenine compounds, only cyclic-AMP and ADP showed significant activity, and these activities were promoted by addition of theophylline to the incubation medium. When aleurone layers of barley endosperm tissues were incubated with GAs in the presence of tannic acid, the amylase activity in the incubation medium was reduced. Cyclic-AMP induced amylase activity was also reduced by additiion of tannic acid. The cyclic-AMP response promoted was more sensitive to tannin inhibition than GAs response. The inhibitory effect of tannic acid shwoed reversibility by addition of higher concentration of GAs or cyclic-AMP. The tannic acid effect on GAs response was also recovered by addition of a higher concentration of cyclic-AMP. Experiment with polyacrylamide disc electrophoresis showed different isozyme patterns according to the additions in the incubation medium. Inhibitory effects of decursinol and coumarin was compared with that of tannic acid. They showed different zymogram patterns.